Lightning-arrester.



PATENTED JUNE 5, 1906.

T. J. JOHNSTON. LIGHTNING ARRESTER. APTLIOATION FILED JULYn 1901 Inventor. v Thomas lJohnsTon.

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Um TED sTArEs PATENT OFFICE.

THOMAS J. JOHNSTON, OF BROOKLYN, NEW YORK, ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION OF NEWV YORK.

LIGHTNING-ARRESTER.

Specification of Letters Patent.

Lia/tented. June 5, 1906.

will therefore pass to earth. This result may 5 5 useful Im rovements in Lightning-Arresters,

of which t e following is a specification.

My present invention relates to lightningarresters, the object being to render more perfeet the protection against lightning or other static discharge.

It frequently happens that apparatus in circuits rotected by ilightning-arresters is damage notwithstanding such present forms of protection, the arresters not fully guarding the apparatus against all kinds of discharges. Even when'the protectors are of improved pattern this damage may result from what are 00110 uially designated as sneak discharges, w ich are probably discharges of such rate of vibration or such wave length as not to be earthed by the protective device. A consideration of the causes at work in a lightning discharge will indicate the reason for this result. The lightning-stroke may develo oscillations of different Wave lengths in t e circuit struck or inductively affected, and obviously the character of the wave may be such that it will not leap the air-gap in the discharge device, or a wave may be of such a length as to develop at the connection of the earth branch to the line a node or point of zero potential, in which case the absence of electromotive force would prevent the discharge being earthed, resulting in probable damage to the ap aratus to be protected, which might be for t at-wave at a point of high otential. Thus a lightningarrest'er in or er to be thoroughly effective should guard against the establishment of such a nodal point at the earth joint and should, moreover, prevent transmission through the protected apparatus of currents of low fre u'ency, such as might traverse an air-core he Withoutmaterial opposition. I accomplish these results by establishing a plurality of grounds or earth branches and interposing in the rotected circuit at the machine side of tfie several grounds devices of different obstructive value, the result being that if wavesof a given frequency are established in the line which might find a nodal pplint at one of the connections it will not d such a point at others, and the discharge be practically effected by interposing obstruc tive devices at different points in the line and varying the value of their impedance, as by a relative difference of length or number of turns or character of coil. may employ a helix having an air-core as one obstructive device, a spiral as another, a helix with a soft-iron core as a third, a helix with a polarized core as another, and I may further multiply the number by varying the number of turns of these types of coil. Earth branches containing spark-gaps may be connected between these coils.

My invention therefore consists in coupling in a line for protection against lightning discharge a plurality of obstructive devices adapted to guard against waves of different rates and connecting earth branches at points between the several devices. The several features of novelty will be more particularly hereinafter described and will be definitely indicated in the claims appended to this specification.

In the accompanying drawing, (which diagrammatically illustrates the invention, )1 1 1 represent a circuit of any length, and 2 a device to be pr0tected-as, for-example, an electric generator in said circuit.

3, 3, 3 and 3 represent a group of protective devices, of which 3 is an ordinary type of lightning-arrester having a magnetic blow-out for extinguishing any are formed by the line-current, and 3, 3 and 3 re resent coils, between which are connecte earth branches 4 4 in which may be interposed ordinary spark-gap lightning-arresters. These would ordinarily be provided with arc-rupturing devices of any a proved type, as is now so well understoo that I have not deemed it' necessary to illustrate them. The equally well-known non-inductive resistance may be provided, as described in the patent to Thomson, No. 493,314. This it seems unnecessary to depict. The coils 3, 3, and 3 are so selected as to have different choking effects for a lightning discharge.

3 represents an air-core helix, 3? a spiral, and 3 a helix containing a magnetic or iron core, which may or may not bepolarized. Coils of the same character may also be duplicated and made of different impedance by varying the number of turns or length. Of the three types shown the air-core helix For example, I'

rangement-where a single obstructive device is provided, since the different coils will choke ofl' currents of different rates of vibration,

' thereby preventing the escape through the generator of sneak discharges, and if by chance a discharge of such a rate as would establish a nodal point at, say, the joint for the branch 4* should .be produced in the line the currents would be earthed throu h the branch 4 or 4*, since the coils being designedly of different values a node would not be likely to form at all these points.

Having thus described my invention, what I claim as new, and desire to protect by Letters Patent of the United States, is

1. A lightning-arrester comprising a plurality of obstructive devices of differing-impedance connected in circuit with the protected device forguarding against Waves of different frequencies, and earth branches connected at points'between the'devices.

different impedance arranged in series in the line, each with a spark-gap in an earth connection on its line side.

5. In a lightning-arrester, the combination of a spiral, an air-core helix and a helix with a core'of magnetic material arranged in serie in the line. and differing in im edance, wit spark-gaps in an earth connection on the line side of each coil.

6. A lightning-arrester com rising a plurality of earth branches and a p urality of obstructive coils of differing impedance connected in series with the protected device and between the protected sides of said branches.

In witness whereof I have hereunto set my hand this 5th day of July, 1901.

THOMAS J. JOHNSTON.

Witnesses:

BENJAMIN B. HULL, DANIEL J. MoNAMARA, Jr 

